(2017-10-02)Wind and solar power are growing as sustainable alternatives to fossil fuels, but storing renewable energy through the night, when the sun isn’t shining, or when no wind is rotating the turbines, remains a hurdle.

A team of scientists at Columbia University has come up with a potential solution, however: using evaporation — the natural process that turns liquid into vapor — to power homes.

Researchers said on Sept. 26 evaporation from U.S. lakes and reservoirs could generate almost 70 percent of the country’s current power output, while saving trillions of gallons of water every year.

“Evaporation can continue throughout the day and night because water can store heat, which is a form of energy,” Ozgur Sahin, a Columbia University professor and lead author of the study, told the Thomson Reuters Foundation in a telephone interview.

“Evaporation comes with a natural battery,” added Ahmet-Hamdi Cavusoglu, another lead author and a graduate student at the New York university. “You can make it your main source of power and draw on solar and wind when they’re available.”

To generate electricity, sponge-like materials are used to capture evaporation from a covered water source, growing bigger as they absorb more moisture.

Later, when the cover on the water source is opened, the materials dry and grow smaller. That change in size can be used to generate energy, the researchers say.

The machine used in the process — the Evaporation Engine — can reduce natural evaporation, saving on the large quantitites of water lost through that process every year.

The study said 25 trillions gallons of water could be saved in the United States each year by using the technology, or about 20 percent of the water people consume in the country.

Sunny states such as California, Nevada and Arizona, which regularly suffer from drought, could benefit most from the process, researchers said.

But the machine has so far only been used in a lab. Researchers now are hoping to make it more efficient and test it on a lake or reservoir, Sahin said.Speech